Photocathode having an intermediate layer between its carrier and its luminous layer

ABSTRACT

A photo cathode consists of a combination of layers, including a carrier layer, a luminous layer and a photo cathode layer. The carrier layer has an intermediate layer upon which the luminous layer is applied. The luminous layer carries the photo cathode layer. The invention is particularly characterized in that the intermediate layer consists of an elastic substance or formchanging substance.

United Stat s Patent 1191 FFanz et al.

1111 3,852,632 Dec. 3,1974

PI-IOTOCATIIODE HAVING AN INTERMEDIATE LAYER BETWEEN ITS CARRIER AND ITS LUMINOUS LAYER Inventors: KarlFranz, Erlangen; Hermann Christgau, Furth; Aribert Stachowiak, Erlangen, all of Germany Siemens Aktiengesellschaft, Munich, Germany Filed: July 10, 1972 Appl. No.; 270,341

Assignee:

[30] Foreign Application Priority Data July [2, I971 Germany 2134762 us. c1. 313/380, 117 335 E, 117/335 0,

1 313/94,313/101 1111.01. non 31/50 Field of Search...' 313/65 R, '65 A, 94, 101; 117/335 R, 33.5 E, 33.5 c

References Cited I UNITED STATES PATENTS 3,300,668 l/l967 Niklas 3l3/65 R 3,558. 893' 1/1971 Ball ....'313/65 R x 3.706385 12/1972 Fister et al. 313/65 R x Primary Examiner-Herman Karl Saalbach Assistant Examiner-Siegfried H. Grimm Attorney, Agent, or Firm-V. Alexander Scher [5 7] ABSTRACT A photo cathode consists of a combination of layers,

including a carrier layer, a luminous layer and a photo cathode layer. The carrier layer has an intermediate layer upon which the luminous layer is applied. The luminous layer carries the photo cathode layer. The invention is particularly characterized in that the intermediate layer consists of an elastic substance or form-changing substance.

9 Claims, 2 Drawing Figures PATENHL 05B 74 PHOTOCATHODE HAVING AN INTERMEDIATE LAYER BETWEEN ITS CARRIER AND ITS LUMINOUS LAYER Known photo cathodes consist of an aluminum plate upon which a luminous layer is steamed on. Then a photo cathode layer containing, for example, alkali metals, can be applied upon the luminous layer. There is then the difficulty that, on the one hand, the carrier layer reflects light and due to stray rays produces images in the luminous layer which are not sharp. On the other hand,' the luminous layer is poorly joined to its carrier. For that reason bases have been used joined by etching. This, however, has the drawback that the base and the luminous substance applied thereon, particularly when aluminum sheets are used as a base, have greatly different coefficients of expansion. For example, when CslzNa is used as the luminous substance and aluminum as the carrier, there is an expansion difference of 1:2. As a rule this produces tears and bends already during the manufacture, which result in an improper image. Furthermore, more or less isolated islands are produced in the photo cathode, which disturb the image by diminution of electrons. Through the tears,-etc., alkali metals usually employed in photo cathodes can reach the aluminum carrier. The reaction which then takes place results at least partially in destructions in the photo cathode which produce further desburbances in thepicture. .An object of the present invention is to improveexisting photo cathodes.

Another object is to provide a luminous layer which will well adhere to the carrier and will not be torn off 7 even after lenghty use, the carrier having an expansion coefficient different from that of the luminous layer.

lnaccordance with the present invention this object,

is realized through the provision of an intermediate layer consisting of .an elastic or plastically changeable 190 to 200 mm. and a curvature depth of about 20 mm.

the speed of rotation at the beginning of the coating process should be about 1,500 rotations andshould be lowered gradually. This assures that the coating with the lacquer will extend smoothly to the edge of the calotte without any stripes.

When aluminum is used as a carrier and'the luminous layer is steamed on, the average coating with artificial resinshould amount to 0.5 to 5 mg/cm, whereby due to the use of sufficiently raw surfaces and suitable artificial substances producing adequate smoothness the best range lies between 1.0 to 1.5 mglcm It is advantageous during the spraying of lacquer to thicken it by blowing with hot air. This provides in a simple manner that even after the termination of the spraying the layer of lacquer will remain uniformly divided upon the surface of the calotte and will not accumulate in the deepest located central point since viscosity rises to a substantial extent due to the volatilization of the solvent and partial condensation of the resin. After the polyimide lacquer has become a uniform dust-dry coating, a heating takes place for about one hour to 110 to 130C, to eliminate the solvent residues. Finally the polyimide .resin is condensed, i.e., hardened, for about 2 hours at a temperature amounting up to 300C. Obviously, the durations for the hardening and for driving out solvent residues are variable within wide limits, specifically they can be extended without a damaging effect upon the results. I

By comparable technology the polyimide resin can be substituted by a silicon resin, for example, methylphenyl siloxane in a suitable solvent, such as toluol or perchlorethylene, and can be sprayed according to the described process. The solution should have from 5 to 10 percent resin in order to have adequate viscosity,

sium iodide which-is activated with sodium (CslzNa) substance which permits shiftings between the carrier and the luminous layer.

The advantageous effect of this construction can be easily explained by the fact that the intermediate layer due to its. capacity of changing its form, balances the expansion properties of the carrier and the luminous layer, since then the two parts are shiftable relatively to each other at least to a certain extent.

When a carrier consisting of aluminum sheets is used, an intermediate layer of sufficient adaptability may consistof polyimide or silicon resin. By way of example, a well holding layer of polyimide is produced when upon a roughened concave surface of an Al-calotte a partially condensed polyimide is applied in the form of a lacquer dissolved indimethyl formamide in a weight ratio-of 1:1 to 1:2. The partially condensed resin is of Y the type used in the trade. The liquid layer is distributed uniformly by the rotation of the calotte having an upwardly directed concave side, the rotation taking place about a verticalaxis extending through the deepwhich is applied in the required layer thicknessFor use with X-rays which are "usedin medical diagnosis, the

thickness should range from 40am to 150um.

. The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawing showing by way of example only, a'preferredembodiment of the innventive idea as used in connection with a vacuum image amplifier.

In the drawing: P16. 1 is a diagrammatic section through image amplifier.

FIG. 2 is a partial section through a carrier provided with an intermediate layer and a luminous layer.

est point of the calotte. in case of a screen diameter of FIG. 1 shows a vacuum container 1 of glass which. contains inthe known manner the photo cathode 2,

electrodes 3 to 5 of the electronic optical imaging device as well as the viewing screen 6.

The photo cathode 2 made in accordance withthe present invention includes a curved carrier, the calotte f an aluminum sheet having a thickness of 0.5

.mm and at a curvature radius of mm. a diameter of 200mm. The calotte 7 carries upon its concave side the intermediate layer 8 upon which lies the luminous layer 9 covered by the photo cathode layer 10.

an X-ray The intermediate layer 8 consists of an elastic or plastically variable polyimide or silicon resin and is applied upon a surface 7' of the carrier 7 which was roughened by etching with muriatic acid according to one of the described processes to a thickness of 1.5 mg/cm The making of the luminous layer 9 is carried out by steaming on the luminous substance CslzNa at less than 10 Torr and a speed of lOum/min. At the end the photo cathode layer of caesium and antimony (CsSb) is steamed on and formed.

As is known, when X-rays or similar transmitting rays pass through the calotte, a light image of the corresponding intensity distribution appears in the luminous layer 9. It provides correspondingly distributed electrodes in the layer 10. By action of voltages applied at the electrodes 3 to 5 the electronic image is formed upon the screen 6. As is known, due to the diminution and acceleration a bright image of rays striking the combination is produced on the screen.

When the screen 6 is produced as a target of a remote vision feeling tube, the advantages of the present invention can be also made useful in remote vision technology.

What is claimed is:

l. A photo cathode, comprising a carrier layer, an intermediate layer carried by said carrier layer and consisting of a deformable material, a luminous layer carried by said intermediate layer and a photo cathode layer carried by said luminous layer.

2. A photo cathode in accordance with claim 1, wherein said intermediate layer consists of an artificial resin.

3. A photo cathode in accordance with claim 2, wherein said artifical resin is a polyimide.

4. A photo cathode in accordance with claim 2, wherein said carrier layer consists of aluminum, said luminous layer consists of caesium iodide/sodium and said intermediate layer is a coating amounting to 0.5 to 5 mg/cm 5. A photo cathode in accordance with claim 4, wherein said coating amounts to 1.0 to 1.5 mglcm 6. A photo cathode in accordance to claim 3 wherein said intermediate layer consists of polyimide hardened on the carrier.

7. A photo cathode in accordance to claim 3 wherein said silicon resin is methylphenyl siloxane.

8. A photo cathode in accordance with claim 2, wherein said artificial resin is a silicon resin.

9. A photo cathode in accordance with claim 3, wherein said intemediate layer consists of silicon resin hardened on the carrier. 

1. A PHOTO CATHODE, COMPRISING A CARRIER LAYER, AN INTERMEDIATE LAYER CARRIER BY SAID CARRIER LAYER AND CONSISTING OF A DEFORMABLE MATERIAL, A LUMINOUS LAYER CARRIED BY SAID INTERMEDIATE LAYER AND A PHOTO CATHODE LAYER CARRIED BY SAID LUMINOUS LAYER.
 2. A photo cathode in accordance with claim 1, wherein said intermediate layer consists of an artificial resin.
 3. A photo cathode in accordance with claim 2, wherein said artifical resin is a polyimide.
 4. A photo cathode in accordance with claim 2, wherein said carrier layer consists of aluminum, said luminous layer consists of caesium iodide/sodium and said intermediate layer is a coating amounting to 0.5 to 5 mg/cm2.
 5. A photo cathode in accordance with claim 4, wherein said coating amounts to 1.0 to 1.5 mg/cm2.
 6. A photo cathode in accordance to claim 3 wherein said intermediate layer consists of polyimide hardened on the carrier.
 7. A photo cathode in accordance to claim 3 wherein said silicon resin is methylphenyl siloxane.
 8. A photo cathode in accordance with claim 2, wherein said artificial resin is a silicon resin.
 9. A photo cathode in accordance with claim 3, wherein said intemediate layer consists of silicon resin hardened on the carrier. 